When a subscriber calls another through a mobile communication network, a terminating exchanger on the network provides the caller with a uniform RBT.
Since the RBT is same all the time, a caller can not identify a called before the called answers. Furthermore, the uniform RBT can not satisfy various subscribers' needs to reveal their personality.
In addition, a mobile communication network provides CWS in commerce. In CWS, however, an exchanger serving a called and a former caller, who are talking each other, provides a latter caller with a uniform RBT, and also provides a uniform CWT, which is different in sound from RBT, for a call waiter who is selected to wait by the called. Therefore, a latter caller can not identify a called before the called answers and the uniform CWT can not satisfy various subscribers' needs to reveal their personality.
On the other hand, various ad methods are being proposed in these days. One of these ad methods is to send an ad sound message to a caller instead of a conventional ringback tone. However, such an ad sound message is chosen unilaterally by a network operating enterprise. If a caller heard such a unilateral ad sound he or she could talk over a mobile telephone with a called for a limited time.
However, the method that an ad sound is provided instead of a conventional RBT still has the aforementioned drawbacks. That is, a caller can not identify a called before the called answers and the uniform RBT can not satisfy various subscribers' needs to reveal their personality as explained above.